1. Field of the Invention
The present general inventive concept relates to an inkjet head having a hydrophobic coating layer, and more particularly, to a method of forming a hydrophobic coating layer on a surface of a nozzle plate of an inkjet head.
2. Description of the Related Art
Generally, inkjet heads are devices for printing an image on a printing medium by ejecting ink droplets onto a desired region of the printing medium. Depending on an ink ejecting method, the inkjet heads can be classified into two types: a thermal inkjet head and a piezoelectric inkjet head. The thermal inkjet head generates bubbles in an ink by using heat and ejects the ink utilizing an expansion of the bubbles, and the piezoelectric inkjet head ejects an ink using pressure generated by deforming a piezoelectric material.
FIG. 1 is a sectional view illustrating a conventional piezoelectric inkjet head, and FIG. 2 is a view illustrating problems caused by a surface treatment failure at a nozzle plate of the conventional piezoelectric inkjet head of FIG. 1.
Referring to FIG. 1, a manifold 11, a plurality of restrictors 12, and a plurality of pressure chambers 13 forming an ink flow channel are formed in a flow channel plate 10 of the piezoelectric inkjet head. A vibration plate 20 which can be deformed by piezoelectric actuators 40 is bonded to a top surface of the flow channel plate 10, and a nozzle plate 30 in which a plurality of nozzles 31 are formed is bonded to a bottom surface of the flow channel plate 10. The vibration plate 20 is formed integrally with the flow channel plate 10, and the nozzle plate 30 is formed integrally with flow channel plate 10.
The manifold 11 is an ink passage supplying an ink from an ink reservoir (not shown) to the respective pressure chambers 13, and the restrictors 12 are ink passages allowing inflow of the ink from the manifold 11 to the pressure chambers 13. The pressure chambers 13 are filled with ink supplied by the manifold 11 and are arranged at one side or both sides of the manifold 11. The nozzles 31 are formed through the nozzle plate 30 and are connected to the respective pressure chambers 13. The vibration plate 20 is bonded to the top surface of the flow channel plate 10 to cover the pressure chambers 13. The vibration plate 20 is deformed by the operation of the piezoelectric actuators 40 to change pressures in the respective pressure chambers 13 to eject ink from the ink chambers 13. Each of the piezoelectric actuators 40 includes a lower electrode 41, a piezoelectric layer 42, and an upper electrode 43 sequentially stacked on the vibration plate 20. The lower electrode 41 is formed on the entire surface of the vibration plate 20 as a common electrode. The piezoelectric layer 42 is formed on the lower electrode 41 above each of the pressure chambers 13. The upper electrode 43 is formed on the piezoelectric layer 42 as a driving electrode for applying a voltage to the piezoelectric layer 42.
In the above-described piezoelectric inkjet head, a surface treatment of the nozzle plate 30 has an effect on the ink ejecting performance of the inkjet head, such as an ink ejecting speed and/or a straightness of the ink ejecting from the nozzles 31. That is, the nozzles 31 should have a hydrophilic surface, and the nozzle plate 30 should have a hydrophobic surface to increase the ink ejecting performance of the inkjet head.
Generally, a hydrophobic coating layer is formed on the nozzle plate 30 according to various known methods. Examples of conventional methods to form a hydrophobic coating layer on the nozzle plate 30 include a dipping method and a depositing method. In the dipping method, the nozzle plate 30 is dipped into a hydrophobic material solution to form a hydrophobic coating layer on the nozzle plate 30. In the depositing method, a hydrophobic material is deposited on the nozzle plate 30.
However, in both conventional coating methods, it is difficult to form a hydrophobic coating layer only on the outer surface of the nozzle plate without forming the hydrophobic coating layer on the inner surfaces of the nozzles 31. That is, the hydrophobic coating layer may be unevenly formed on the inner surfaces of the nozzles 31. In this case, as illustrated in FIG. 2, ink droplets may not be ejected straight from the nozzles 31, and a speed and volume of the ejected droplets may not be uniformly distributed, thereby deteriorating the ink ejecting performance of the inkjet head.